Roller leveler and sheet-material flattening method

ABSTRACT

A roller leveler for flattening sheet material includes: a leveling roll unit that has a plurality of leveling rolls configured to rotate so as to pass the sheet material while sandwiching and pressing the sheet material interposed therebetween; pushing cylinders configured to press the sheet material via the leveling rolls and provided on each of an entrance side and a discharge side of the leveling roll unit, on which the sheet material enters and is discharged into and from the leveling roll unit, respectively; and a driving mechanism configured to rotate the leveling rolls to pass the sheet material, wherein the plurality of leveling rolls are designed so that a diameter thereof satisfies a relation, 0.5&lt;D/P&lt;0.9, in relation to a roll pitch P of the leveling rolls that is determined from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material to be flattened.

TECHNICAL FIELD

The present invention relates to a roller leveler for flattening metal sheet material, such as steel sheet material, and a sheet-material flattening method.

BACKGROUND ART

In the process of manufacturing sheet material, such as steel sheet material, the sheet material is subjected to rolling and cooling steps, in which the sheet material undergoes deformation, such as warping and/or waving. Accordingly, in order to remedy the deformation, such as warping and/or waving, and thereby to flatten the sheet material, a roller leveler including a plurality of leveling rolls disposed on upper and lower sides in a staggered manner, is used (Patent Document 1, for example).

The roller leveler passes sheet material to be flattened, with the upper leveling rolls being caused to penetrate between the lower leveling rolls or the lower leveling rolls being caused to penetrate between the upper leveling rolls, to repeatedly bend the sheet material, and thereby to planarize the warping and/or waving of the sheet material.

In such a roller leveler, the roll pitch of the leveling rolls is determined from the maximum requirement yield stress and the corresponding maximum requirement sheet-material thickness of the sheet material to be flattened. The maximum flattening force (pressing force) and the maximum torque are determined from the determined roll pitch. Conventionally, in relation to the roll pitch determined in this way, the diameter of the leveling rolls is set as large as possible, that is, set equal to or greater than 0.9 times of the roll pitch and smaller than the roll pitch, in order to make it sufficiently easy to pass the sheet material and to transmit sufficient torque. Note that while the maximum requirement yield stress and the maximum requirement sheet-material thickness mean the maximum values of the yield stress and the sheet-material thickness that are required as specifications of the sheet material by a user. These terms are used for the sake of simplicity in the following description. Note that the reason why the roll pitch is determined from the yield stress and the sheet-material thickness of the sheet material to be flattened will be described in detail in the section, [Embodiment for Carrying Out the Invention].

PRIOR ART DOCUMENT Patent Document

[Patent Document 1]

Japanese Patent Application Publication No. 2009-255148 (JP 2009-255148 A)

SUMMARY OF INVENTION Problems to be Solved by the Invention

In recent years, however, the demand for leveling or flattening sheet material that is thinner and greater in yield stress as compared to conventionally used sheet material has been increasing and, when a conventional roller leveler using large-diameter rolls as described above is employed, there can be a case where sufficiently large pressing amount cannot be achieved. For this reason, there is an increasing demand for a roller leveler that can sufficiently flatten a thin, high-yield stress sheet material.

The present invention has been made under such circumstances and an object of the present invention is to provide a roller leveler and a sheet-material flattening method, with which it is possible to perform leveling or flattening of metal sheet material, such as steel sheet material, that is thin and has a high yield stress.

Means for Solving the Problems

In order to solve the above problems, a first aspect of the present invention provides a roller leveler for flattening sheet material by passing the sheet material through a pass line, the roller leveler including: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a pushing cylinder configured to press the sheet material via the leveling rolls and provided on each of an entrance side and a discharge side of the leveling roll unit, on which the sheet material enters and is discharged into and from the leveling roll unit, respectively; a plurality of backup rolls that back up the leveling rolls; and a driving mechanism configured to rotate the leveling rolls to pass the sheet material, wherein the plurality of leveling rolls are designed so that a diameter D thereof satisfies a relation, 0.5<D/P<0.9, in relation to a roll pitch P of the leveling rolls that is determined from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material.

In the above first aspect, it is preferable that the roller leveler further include a control unit that is configured to control an amount of pressing of the sheet material performed by the pushing cylinder so that the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, wherein the control unit has a catch correction table, in which a catch limit pressing amount and a catch correction control distance depending on thickness of the sheet material are entered, the catch limit pressing amount being a pressing amount, at or under which the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, the catch correction control distance being an amount of travel of a leading edge of the sheet material, at which the pressing amount should be brought to the catch limit pressing amount, and the control unit be configured so that when a specified pressing amount, required to flatten the sheet material, of the pushing cylinder on the entrance side is greater than the catch limit pressing amount, the control unit performs control based on the catch correction table so that the pressing amount of the pushing cylinder on the entrance side is limited to the catch limit pressing amount until the leading edge of the sheet material reaches the catch correction control distance and, when the leading edge of the sheet material reaches the catch correction control distance, the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount. In this case, it is preferable that pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance, be entered in the catch correction table, and the control unit control the pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is changed from the catch limit pressing amount to the specified pressing amount, based on the catch correction table.

A second aspect of the present invention provides a roller leveler for flattening sheet material by passing the sheet material through a pass line, the roller leveler including: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a plurality of backup rolls that back up the plurality of leveling rolls from upper and lower sides; a pair of roll frames that support the leveling rolls and the backup rolls from upper and lower sides; a pair of frames that support the pair of roll frames from upper and lower sides; a pushing cylinder provided on each of an entrance side and a discharge side, at which the sheet material enters and is discharged into and from the leveling roll unit, respectively, and configured to push a working frame, which is one of the pair of frames, toward the pass line so as to press the sheet material between the leveling rolls via a corresponding one of the pair of roll frames; a driving mechanism configured to rotate the leveling rolls; a plurality of hydraulic crowning cylinders installed so as to be lined up in a width direction perpendicular to a direction, in which the sheet material is passed, between the working frame and the corresponding one of the pair of roll frames; and a control unit that controls flattening of the sheet material, wherein the plurality of leveling rolls are designed so that a diameter D thereof satisfies a relation, 0.5<D/P<0.9, in relation to a roll pitch P of the leveling rolls that is determined from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material, and the control unit is configured to perform control so that the sheet material is passed between the leveling rolls via the driving mechanism while controlling an amount of pressing performed by the pushing cylinders, and is also configured to perform tightening control, in which amounts of lateral deflection of the pair of frames in the width direction are determined, an amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the amounts of lateral deflection is calculated, and tightening of each of the hydraulic crowning cylinders is controlled based on the required amount of tightening.

In the above second aspect, it is preferable that, based on information on compressive deformation of the pushing cylinders, the hydraulic crowning cylinders, the pair of roll frames, the backup rolls, and the leveling rolls, the control unit calculate a required amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the compressive deformation and perform the tightening control of each of the hydraulic crowning cylinders based on a total value obtained by summing both this required amount of tightening and the required amount of tightening that is required to compensate for the amounts of lateral deflection of the pair of frames.

In the above second aspect, it is preferable that the control unit have a catch correction table, in which a catch limit pressing amount and a catch correction control distance depending on thickness of the sheet material are entered, the catch limit pressing amount being a pressing amount, at or under which the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, the catch correction control distance being an amount of travel of a leading edge of the sheet material, at which the pressing amount should be brought to the catch limit pressing amount, and the control unit be configured so that when a specified pressing amount, required to flatten the sheet material, of the pushing cylinder on the entrance side is greater than the catch limit pressing amount, the control unit performs control based on the catch correction table so that the pressing amount of the pushing cylinder on the entrance side is limited to the catch limit pressing amount until the leading edge of the sheet material reaches the catch correction control distance and, when the leading edge of the sheet material reaches the catch correction control distance, the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount. In this case, it is preferable that pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance, be entered in the catch correction table, and the control unit control the pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is changed from the catch limit pressing amount to the specified pressing amount, based on the catch correction table.

In the above first and second aspects, it is preferable that the diameter D and the pitch P satisfy a relation, 0.55<D/P<0.8.

It is preferable that the driving mechanism include: an upper leveling roll-driving section that has upper leveling roll-driving motors for driving the upper leveling rolls and upper leveling roll power-transmitting part for transmitting power of the upper leveling roll-driving motors to the upper leveling rolls; and a lower leveling roll-driving section that has lower leveling roll-driving motors for driving the lower leveling rolls and lower leveling roll power-transmitting part for transmitting power of the lower leveling roll-driving motors to the lower leveling rolls, wherein the upper leveling roll power-transmitting part and the lower leveling roll power-transmitting part are disposed so as not to interfere with each other.

A third aspect of the present invention provides a sheet-material flattening method of flattening sheet material via a roller leveler for flattening the sheet material by passing the sheet material through a pass line, wherein the roller leveler includes: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a pushing cylinder configured to press the sheet material via the leveling rolls and provided on each of an entrance side and a discharge side of the leveling roll unit, on which the sheet material enters and is discharged into and from the leveling roll unit, respectively; a plurality of backup rolls that back up the leveling rolls; and a driving mechanism configured to rotate the leveling rolls to pass the sheet material, the method including: determining a roll pitch P of the plurality of leveling rolls from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material to be flattened; and setting a value of diameter D of the plurality of leveling rolls so as to satisfy a relation, 0.5<D/P<0.9.

A fourth aspect of the present invention provides a sheet-material flattening method of flattening sheet material via a roller leveler for flattening the sheet material by passing the sheet material through a pass line, wherein the roller leveler includes: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a plurality of backup rolls that back up the plurality of leveling rolls from upper and lower sides; a pair of roll frames that support the leveling rolls and the backup rolls from upper and lower sides; a pair of frames that support the pair of roll frames from upper and lower sides; a pushing cylinder provided on each of an entrance side and a discharge side, at which the sheet material enters and is discharged into and from the leveling roll unit, respectively, and configured to push a working frame, which is one of the pair of frames, toward the pass line so as to press the sheet material between the leveling rolls via a corresponding one of the pair of roll frames; a driving mechanism configured to rotate the leveling rolls; and a plurality of hydraulic crowning cylinders installed so as to be lined up in a width direction perpendicular to a direction, in which the sheet material is passed, between the working frame and the corresponding one of the pair of roll frames, the method including: determining a roll pitch P of the plurality of leveling rolls from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material to be flattened; setting a value of diameter D of the plurality of leveling rolls so as to satisfy a relation, 0.5<D/P<0.9; determining amounts of lateral deflection of the pair of frames in the width direction; calculating an amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the amounts of lateral deflection; and controlling tightening of each of the hydraulic crowning cylinders based on the required amount of tightening.

In the above fourth aspect, it is preferable that the method further include: based on information on compressive deformation of the pushing cylinders, the hydraulic crowning cylinders, the pair of roll frames, the backup rolls, and the leveling rolls, calculating a required amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the compressive deformation; and controlling tightening of each of the hydraulic crowning cylinders based on a total value obtained by summing both this required amount of tightening and the required amount of tightening that is required to compensate for the amounts of lateral deflection of the pair of frames.

In the above third and fourth aspects, it is preferable that, based on a catch correction table, in which a catch limit pressing amount and a catch correction control distance depending on thickness of the sheet material are entered, the catch limit pressing amount being a pressing amount, at or under which the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, the catch correction control distance being an amount of travel of a leading edge of the sheet material, at which the pressing amount should be brought to the catch limit pressing amount, the following be further performed: limiting the pressing amount of the pushing cylinder on the entrance side to the catch limit pressing amount until the leading edge of the sheet material reaches the catch correction control distance when a specified pressing amount, required to flatten the sheet material, of the pushing cylinder on the entrance side is greater than the catch limit pressing amount; and bringing the pressing amount of the pushing cylinder on the entrance side to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance. In this case, it is preferable that the method further include: entering into the catch correction table pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance; and controlling the pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is changed from the catch limit pressing amount to the specified pressing amount, based on the catch correction table.

Effects of Invention

According to the present invention, the value of the diameter D of the plurality of leveling rolls is set so as to satisfy the relation, 0.5<D/P<0.9, in relation to the roll pitch P of the leveling rolls that is determined from the maximum requirement yield stress and the corresponding maximum requirement sheet-material thickness of the sheet material to be flattened. For this reason, it is possible to strongly bend the sheet material by increasing the pressing amount. Consequently, it is made possible to perform leveling or flattening of sheet material that is thin and has a high yield stress and a higher degree of flatness is achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view showing a roller leveler according to an embodiment of the present invention;

FIG. 2 is a front view showing the roller leveler according to the embodiment of the present invention;

FIG. 3 is a diagram for explaining a relation between a roll diameter and a roll pitch of the roller leveler according to the embodiment of the present invention;

FIG. 4 is a diagram for explaining a driving mechanism of the roller leveler according to the embodiment of the present invention;

FIG. 5 is a sectional view for explaining a structure of a hydraulic crowning cylinder of the roller leveler according to the embodiment of the present invention;

FIG. 6 is a block diagram of a control unit of the roller leveler according to the embodiment of the present invention;

FIG. 7 is a diagram showing a catch correction table input into the control unit of the roller leveler according to the embodiment of the present invention;

FIG. 8 is a diagram, in which the abscissa indicates sheet-material thickness and the ordinate indicates yield stress, showing a region, in which flattening can be performed when the plastification ratio is 70% (0.7) in the case of D/P=0.923 and in the case of D/P=0.667;

FIG. 9 is a diagram illustrating control of pressing amount at the time of correction for catching; and

FIG. 10 is a diagram showing a state where a setup to specified pressing amount is performed after correction for catching is completed.

EMBODIMENT FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a side view of a roller leveler according to an embodiment of the present invention, and FIG. 2 is a front view thereof. The roller leveler 100 of the present embodiment includes a housing 1, an upper frame 2 provided inside the housing 1, and a lower frame 3 provided so as to support the housing 1. An upper roll frame 5 is hung under the upper frame 2 via upper roll gripping cylinders (not shown). Meanwhile, a lower roll frame 10 is provided above the lower frame 3. The upper frame 2 is vertically pushed and moved with the use of pushing cylinders (also referred to as “pressing cylinders”) as described later and therefore, the upper frame 2 can be called “working frame”. The working frame is not limited to the upper frame 2. A configuration may be adopted, in which the lower frame 3 is configured as the working frame and the lower frame 3 is vertically pushed and moved with the use of pushing cylinders provided under the lower frame 3.

Provided between the upper roll frame 5 and the lower roll frame 10 is a leveling roll unit 20 including a plurality of upper leveling rolls 6 and a plurality of lower leveling rolls 8 that are arranged on upper and lower sides in a staggered manner so as to form a pass line of sheet material S, which is metal sheet material, such as steel sheet material, between the upper and lower leveling rolls 6 and 8. In the leveling roll unit 20, the upper leveling rolls 6 are supported by the upper roll frame 5 under the upper roll frame 5, and the lower leveling rolls 8 are supported by the lower roll frame 10 above the lower roll frame 10. Guide rolls 14 for guiding the sheet material S are provided on the upstream side and the downstream side of the leveling roll unit 20 with respect to the transfer direction, in which the sheet material S is transferred. The upper leveling rolls 6 and the lower leveling rolls 8 are configured to be rotated by a driving mechanism 15 and can perform leveling operation while passing the sheet material S in one of the direction indicated by an arrow A and the direction indicated by an arrow B in FIG. 1, for example.

A plurality of short-length upper backup rolls 7 for backing up the upper leveling rolls 6 are arranged along the axial direction of the upper leveling rolls 6 above the upper leveling rolls 6 so as to be supported by the upper roll frame 5. A plurality of short-length lower backup rolls 9 for backing up the lower leveling rolls 8 are arranged along the axial direction of the lower leveling rolls 8 below the lower leveling rolls 8 so as to be supported by the lower roll frame 10.

As described above, the roll pitch of both the upper and lower leveling rolls 6 and 8 is determined from the maximum requirement yield stress and the corresponding maximum requirement sheet-material thickness of the sheet material S to be flattened (the maximum value of the yield stress and the maximum value of the sheet-material thickness required in the specifications of the sheet material by a user). This is because leveling force required of the roller leveler 100 is calculated using the following equation (1) from the sheet-material thickness and the yield stress required by the user.

F=2×{3−(1−η)²}×(W×σy×T ²)/(3000×L)×α  (1)

In this equation, F is leveling force, η is plastification ratio, W is sheet-material width (mm), σy is yield stress (kgf/mm²), T is sheet-material thickness (mm), L is roll pitch (mm), and α is a coefficient obtained by actual measurement.

In other words, the leveling force is proportional to the yield stress σy, proportional to the square of the sheet-material thickness T, and inversely proportional to the roll pitch L. This can be simplified and expressed by the equation (2), F=K₁×T²×σy/L, where K₁ is a coefficient.

On the other hand, the leveling force achieved by the roller leveler increases as the diameter of the backup rolls (corresponding to the upper and lower backup rolls 7 and 9) disposed outside the leveling rolls increases. However, the maximum diameter of the backup rolls is almost equal to the roll pitch L because it is impossible for the backup rolls to have a diameter greater than the roll pitch L. For this reason, the maximum value of the leveling force achieved by the roller leveler can be expressed by the equation (3), F=K₂×L, where K₂ is a coefficient.

Combination of equations (2) and (3) results in K₂×L=K₁×T²×σy/L, from which the following equation (4) is derived. The equation (4) indicates that the roll pitch L of both the upper and lower leveling rolls 6 and 8 is determined from the yield stress σy and the sheet-material thickness T of the sheet material S to be flattened.

L={(K ₁ ×T ² ×σy)/K ₂}^(1/2)  (4)

Conventionally, in order to make it sufficiently easy to pass the sheet material and to transmit sufficient torque, the diameter of the leveling rolls is set as large as possible, that is, set equal to or greater than 0.9 times of the roll pitch and smaller than the roll pitch.

In the leveling roll unit 20 according to this embodiment of the present invention, however, as shown in FIG. 3, the roll pitch P (corresponding to the pitch L in the equation (4)) and the roll diameter D of both the upper and lower leveling rolls 6 and 8 are arranged so as to satisfy the relation, 0.5<D/P<0.9. In other words, the roll diameter D is set smaller than the conventional range, 0.9≦D/P<1.0. The value of D/P is preferably within a range, 0.55<D/P<0.8, and is more preferably within a range, 0.6<D/P<0.7.

Pressing cylinders (also referred to as “pushing cylinders”) 4 a and 4 b for applying pressing force (also referred to as “pushing force”) to flatten the sheet material S are arranged at end portions of the leveling roll unit 20 in the transfer direction of the sheet material S, between the housing 1 and the upper frame 2. The pressing cylinders 4 a and 4 b, each including two cylinders, are provided at two ends (driving side and working side) in the width direction of the sheet material S (see FIG. 2, in which, however, only the pressing cylinders 4 a are shown).

Note that, in this specification, the term “press” is intended to include not only a case where the pressure is applied downward as shown in FIG. 1 but also a case where the pressure is applied upward as explained later in a modification. In other words, the term “press” can be replaced with the term “push” in this specification.

The pressing cylinders 4 a and 4 b are configured to press down the sheet material S via the upper roll frame 5, the upper backup rolls 7, and the upper leveling rolls 6 toward the lower leveling rolls 8 provided on the lower roll frame 10 in a stationary manner.

The upper leveling rolls 6 and the lower leveling rolls 8 are configured to be rotated by the driving mechanism 15. In FIG. 1, the driving mechanism 15 is illustrated as if the driving mechanism 15 is connected to the whole of each of the rows of the upper and lower leveling rolls 6 and 8 for the sake of convenience. In actuality, however, the driving mechanism 15 is configured to individually rotate the upper leveling rolls 6 and the lower leveling rolls 8 as described later. The sheet material S is passed between the upper leveling rolls 6 and the lower leveling rolls 8 with the use of the driving mechanism 15 and is pressed down by the pressing cylinders 4 a and 4 b via the upper leveling rolls 6 to level or flatten the sheet material S.

When the sheet material S is transferred in the direction indicated by the arrow A in FIG. 1, the pressing cylinder 4 a functions as the entrance-side pressing cylinder and the pressing cylinder 4 b functions as the discharge-side pressing cylinder. On the other hand, when the sheet material S is transferred in the direction indicated by the arrow B, the pressing cylinder 4 b functions as the entrance-side pressing cylinder and the pressing cylinder 4 a functions as the discharge-side pressing cylinder. Note that the upper leveling rolls 6 may be provided in a stationary manner and the lower leveling roll 8 may be pressed by the pressing cylinders.

As shown in FIG. 4, the driving mechanism 15 includes: an upper leveling roll-driving section 30 having a driving motor 32 and a universal spindle 31 serving as a power-transmitting part connected to a protruding portion 6 a of the shaft of each of the upper leveling rolls 6; and a lower leveling roll-driving section 40 having a driving motor 42 and a universal spindle 41 serving as a power-transmitting part connected to a protruding portion 8 a of the shaft of each of the lower leveling rolls 8. The universal spindles 31 and 41 each transmit power to a portion that is not coaxial with the driving side. The universal spindle 31 has a pair of cross-pin units 33 and 34 and an intermediate shaft 35 interposed therebetween. The universal spindle 41 has a pair of cross-pin units 43 and 44 and an intermediate shaft 45 interposed therebetween. The shaft of the motor 32 and the cross-pin unit 34 on the motor 32-side are connected via a shaft 32 a. The shaft of the motor 42 and the cross-pin unit 44 on the motor 42-side are connected via a shaft 42 a.

As described above, since the diameter D of the upper leveling rolls 6 and the lower leveling rolls 8 is small, the universal spindles 31 and 41 are arranged so as not to interfere with each other in order to avoid the situation where the universal spindles 31 and 41 of the upper leveling roll 6 and the lower leveling roll 8 that are next to each other interfere with each other, the universal spindles 31 and 41 serving as power-transmitting parts of the upper leveling roll 6 and the lower leveling roll 8. Specifically, in order to avoid the situation where the roll-side cross-pin units 33 and 43 of the universal spindles 31 and 41 interfere with each other, the length of the protruding portion 6 a of the upper leveling roll 6 and the length of the protruding portion 8 a of the lower leveling roll 8 are set different from each other so that the cross-pin units 33 and 43 are staggered.

A plurality of hydraulic crowning cylinders 12 (seven cylinders in this embodiment) are coupled to the upper frame 2 and the upper roll frame 5 between these frames, lined up in the sheet-material-width direction. As shown in FIG. 2, the crowning cylinders 12 are installed with even pitches so as to correspond to the upper leveling rolls 6 and the lower leveling rolls 8 along the width direction perpendicular to the direction, in which the sheet material S is passed. The hydraulic crowning cylinders 12 are installed in two rows as shown in FIG. 1. The number of rows of the crowning cylinders, however, may be one or may be three or more.

As shown in FIG. 5, each of the hydraulic crowning cylinders 12 has a cylinder body 51 and a piston 52. The upper end of the piston 52 is coupled to the upper frame 2 via a spherical coupling member 53 and the bottom of the cylinder body 51 is coupled to the upper roll frame 5 via a slide coupling 54. A position sensor 55 is built in each of the hydraulic crowning cylinders 12. Each of the hydraulic crowning cylinders 12 is configured to be telescoped hydraulically and is connected to an oil feed line 56 for feeding oil to an extending-side oil chamber (now shown) for extending operation and to a release line 57 for releasing the hydraulic pressure. A pressure sensor 58 for detecting the hydraulic pressure in the extending-side oil chamber and a control valve 59 for controlling the amount of oil to be fed are connected to the oil feed line 56. A servo valve or a proportional control valve is used as the control valve 59.

As shown in FIG. 2, deflection-detecting sensors 21 for detecting the lateral deflection of the upper frame 2 are provided at central positions with respect to the lateral direction, above the upper frame 2. As shown in FIG. 1, two deflection-detecting sensors 21 are provided along the pass line of the sheet material S. The deflection-detecting sensors 21 continuously detect the distances to the bottom portion of the upper frame 2, based on which distances the amount of deflection of the upper frame 2 is calculated. Deflection-detecting sensors 22 are installed in the inner space in the lower frame 3. In this embodiment, two deflection-detecting sensors 22 are provided along the pass line of the sheet material S at central positions with respect to the lateral direction. The deflection-detecting sensors 22 continuously detect the distances to the ceiling portion of the lower frame 3, based on which distances the amount of deflection of the lower frame 3 is calculated. A configuration may be adopted, in which one of the upper and lower frames 2 and 3 is provided with deflection-detecting sensors and the amount of deflection of the other frame is determined with the use of proportion.

A load cell (or hydraulic pressure converter) 23 is installed between the housing 1 and each of the pressing cylinders 4 a and 4 b. By doing so, it is made possible to detect the compressive deformation of the pressing cylinders 4 a and 4 b, the hydraulic crowning cylinders 12, the upper roll frame 5, the upper backup rolls 7, the upper leveling rolls 6, the lower leveling rolls 8, the lower backup rolls 9, and the lower roll frame 10.

The roller leveler 100 of this embodiment is configured so that components of the roller leveler 100 are controlled by a control unit 60. The control unit 60 includes a process controller having a central processing unit (CPU). The control unit 60 further includes a user interface, such as a keyboard and a display, and a memory, in which recipes containing, for example, processing condition data and control programs (software) are stored, the user interface and the memory being connected to the CPU. A selected recipe is called from the memory in accordance with the instructions from the user interface, for example, and is executed by the process controller. In this way, desired processes (a sequence of operations) are performed by the roller leveler 100 under the control of the process controller. The recipes, containing control programs, processing condition data, etc., that are stored in a computer-readable storage medium, such as a magnetic disk (flexible disk, hard disk, etc.), an optical disk (CD, DVD, etc.), a magneto-optical disk (MO etc.), and a semiconductor memory, can be used. Alternatively, the recipes that are transmitted from another device via a dedicated line, for example, as needed may be used online.

The control unit 60 is configured to control the driving mechanism 15 and the amounts of penetration of the leveling rolls 6 and 8 by the pressing cylinders 4 a and 4 b for the purpose of flattening (leveling) of the sheet material S according to the control programs stored in a computer-readable storage medium. Moreover, the control unit 60 is configured to perform the lateral deflection compensation and the compression compensation of the frames by controlling the tightening of the hydraulic crowning cylinders 12. Furthermore, the control unit 60 is configured to perform pressing control, correction control for catching in particular, of the pressing cylinders 4 a and 4 b.

FIG. 6 shows a block diagram of control performed by the control unit 60. Crowning control, pressing control, and correction control for catching will mainly be described hereinafter. The control unit 60 includes an upper controller 62, a crowning controller 64, and a pressing-and-catching controller 66, each having a microprocessor. The upper controller 62 is configured to control the entire system of the roller leveler 100. The crowning controller 64 is configured to control operation of the hydraulic crowning cylinders 12 based on the instruction from the upper controller 62. The pressing-and-catching controller 66 is configured to perform pressing control, correction control for catching in particular, of the pressing cylinders 4 a and 4 b.

The detection values from the above described deflection-detecting sensors 21 and 22, the load cells 23, the position sensors 55, and the pressure sensors 38 are input to the crowning controller 64. The crowning controller 64 continuously determines the amounts of lateral deflection of the upper and lower frames 2 and 3 based on the detection values from the deflection-detecting sensors 21 and 22 and calculates the amount of extension, that is, the tightening amount of each of the hydraulic crowning cylinders 12 that is required to compensate for the lateral deflection of the frames. In addition, the crowning controller 64 continuously determines the compressive deformation of the pressing cylinders 4, the hydraulic crowning cylinders 12, the upper roll frame 5, the upper backup rolls 7, the upper leveling rolls 6, the lower leveling rolls 8, the lower backup rolls 9, and the lower roll frame 10 based on the detection values from the load cells 23 provided between the housing 1 and the pressing cylinders 4 a and 4 b and calculates the amount of extension, that is, the tightening amount of each of the hydraulic crowning cylinders 12 that is required to compensate for the compressive deformation of these components. The crowning controller 64 sums up these tightening amounts and calculates output signals set so as to feed the pressurized oil having the corresponding pressure to each of the hydraulic crowning cylinders 12. The output signals are fed-back to the control valves 59 to control the hydraulic crowning cylinders 12 so as to minimize the lateral deflection and the compressive deformation.

Pressing amounts (penetration amounts) of the pressing cylinders 4 a and 4 b required to perform leveling (flattening) of the sheet material S, depending on the thickness of the sheet material S, etc., are set in the pressing-and-catching controller 66. When the pressing amount (specified pressing amount) specified, or set, for the entrance-side pressing cylinders (pressing cylinders 4 a when the transfer direction of the sheet material S is the direction A) exceeds the pressing amount (catch limit pressing amount) that is a limit value, at or under which the sheet material S is caught, a failure in catching the sheet material S between the upper leveling rolls 6 and the lower leveling rolls 8, that is, a catch failure occurs. For this reason, in order to prevent such a catch failure, a catch correction table that is a table for correction control for catching as illustrated in FIG. 7 is input in the pressing-and-catching controller 66. The catch correction table is input via a touch panel of an operating section (not shown) or read from a storage medium storing the catch correction table.

In the catch correction table shown in FIG. 7, catch limit pressing amount δL (mm), catch correction control distance Lb (mm), and pressing correction speed IV (mm/sec) are set for each of the ranges of the sheet-material thickness. When the setting value of the pressing amount (penetration amount) of the entrance-side pressing cylinders exceeds the catch limit pressing amount δL, the catch correction control is performed using the catch correction table shown in FIG. 7. Specifically, the pressing-and-catching controller 66 performs control to keep the pressing amount at the catch limit pressing amount δL until the sheet material S is caught and the leading edge of the sheet material S reaches a distance of Lb from the peak of the reference leveling roll (the leftmost leveling roll when the transfer direction is the direction A), and the pressing-and-catching controller 66 performs control to bring the pressing amount (penetration amount) of the entrance-side pressing cylinders to the specified pressing amount at the pressing correction speed IV entered in the catch correction table after the leading edge of the sheet material S is caught by a distance of Lb from the reference leveling roll. A plurality of optical sensors (not shown) for detecting the position of the leading edge of the sheet material S are disposed along the pass line in the leveling roll unit 20, so that the position information of this sheet material S is obtained by detecting the leading edge of the sheet material S with the use of these sensors and tracking the leading edge of the sheet material S with the use of a pulse generator (not shown).

Next, description will be given of operation performed when the sheet material S is flattened by the roller leveler 100 configured as described above.

The sheet material S is transferred from the upstream side of the leveling roll unit 20 of the roller leveler 100 to the leveling roll unit 20, with the sheet material S being guided by the guide roll 14, and is inserted between the upper leveling rolls 6 and the lower leveling rolls 8. When the direction of transfer of the sheet material S coincides with the direction A, the sheet material S is transferred to the leveling unit 20 from the left side in FIG. 1, that is, the pressing cylinders 4 a are the entrance-side pressing cylinders.

In this case, the pressing amounts (penetration amounts) of the pressing cylinders 4 a and 4 b that are required to level (flatten) the sheet material S, depending on the thickness of the sheet material S, etc., are set in the control unit 60. The sheet material S is passed between the upper leveling rolls 6 and the lower leveling rolls 8 by the driving force applied by the driving mechanism 15 while pressing the sheet material S at the specified pressing amount (penetration amount), whereby the sheet material S is flattened.

As described above, the roll pitch P of both the upper and lower leveling rolls 6 and 8 is determined from the maximum requirement yield stress and the corresponding maximum requirement sheet-material thickness of the sheet material to be flattened. The roll diameter D is determined so as to satisfy the relation, 0.5<D/P<0.9, in relation to the determined pitch P. The maximum torque corresponding to the roll pitch P of both the upper and lower leveling rolls 6 and 8 is determined and the load conditions are then determined.

Conventionally, in order to make it sufficiently easy to pass the sheet material and to transmit sufficient torque, the diameter D of the leveling rolls is set as large as possible relative to the roll pitch P of both the upper and lower leveling rolls 6 and 8, that is, set equal to or greater than 0.9 times of the roll pitch and smaller than the roll pitch, satisfying the relation, 0.9≦D/P<1.0. The greater the diameter of the leveling rolls is, the smaller the radius of bending of the sheet material to be passed is. As a result, the maximum pressing amount is reduced and it becomes easy to pass the sheet material. Moreover, it becomes possible to use a large universal joint, which makes it easy to obtain a large maximum torque. For this reason, it has been a common practice to employ the setting satisfying the relation, 0.9≦D/P<1.0.

In recent years, however, the demand for leveling or flattening sheet material that is thinner and greater in yield stress as compared to conventionally used sheet material has been increasing and, when the diameter D of the upper leveling rolls 6 and the lower leveling rolls 8 is set large so as to satisfy the relation, 0.9≦D/P, there can be a case where sufficiently large pressing amount cannot be obtained, that is, sufficient degree of leveling or flattening cannot be performed for sheet material that is thin and has a high yield stress.

In order to flatten the sheet material S by reducing the internal stress of the sheet material S with the use of the driving force of the leveling rolls 6 and 8, it is necessary to satisfy the following equation (5), where thickness of the sheet material S is T (mm), Young's modulus is E (N/mm²), yield stress is σy (N/mm²), roll diameter is D (mm), and plastification ratio is η.

1−η=(σy×D)/(E×T)  (5)

In order to sufficiently reduce the internal stress, the plastification ratio is required to be equal to or greater than 0.7, that is, it is required to satisfy the following relation (6).

0.3≧(σy×D)/(E×T)  (6)

This relation can be transformed into the following relation (7).

D≦0.3(E×T)/σy  (7)

This indicates that the smaller the sheet-material thickness T is and the greater the yield stress σy is, the smaller the diameter of the leveling rolls should be set. However, conventional idea has been limited to reduction of the diameter D within the range, 0.9≦D/P. In this case, however, torque is limited and it may become impossible to pass the sheet material.

The present inventor, however, has found that, despite the conventional common practice, it is possible to perform leveling or flattening even when leveling rolls with small diameter satisfying the relation, D/P<0.9, in relation to the roll pitch P that is determined from the maximum requirement yield stress and the corresponding maximum requirement sheet-material thickness of the sheet material to be flattened, and use of leveling rolls having such a small diameter increases the pressing amount, which makes it possible to level or flatten sheet material that is so thin and high in yield stress that it could not be sufficiently flattened by conventional method.

Note that the roll diameter D is determined so as to satisfy the relation, 0.5<D/P<0.9, in relation to the roll pitch P because the sheet material does not bend along the rolls, that is, the radius of bending of the sheet material does not decrease according to the roll diameter when the value of D/P is equal to or smaller than 0.5.

The roll pitch P of both the upper and lower leveling rolls 6 and 8 is determined from the maximum requirement yield stress and the corresponding maximum requirement sheet-material thickness of the sheet material to be flattened, and the maximum torque is also determined from the pitch P. For this reason, the cross-pin units 33, 34, 43, and 44 of the universal spindles 31 and 41 that have the size corresponding to the maximum torque are used. When conventional leveling rolls that have a diameter satisfying the relation, D/P≧0.9, are used, the diameter of the cross-pin unit is slightly smaller than the diameter of the leveling rolls. In this embodiment, however, the diameter D of the upper leveling rolls 6 and the lower leveling rolls 8 satisfies the relation, D/P<0.9, that is, the diameter D is smaller as compared to the conventional cases. As a result, when the universal spindles 31 and 41 are arranged so as to overlap with each other as in the conventional cases, there is a possibility that the roll-side cross-pin units 33 and 43 of the adjacent upper and lower leveling rolls 6 and 8 interfere with each other. Thus, the length of the protruding portions 6 a of the shafts of the upper leveling rolls 6 and the length of the protruding portions 8 a of the shafts of the lower leveling rolls 8 are set different from each other so that the cross-pin units 33 and 43 are staggered to be prevented from interfering with each other. Conventionally, it has been a problem that reduction of the diameter of the leveling rolls makes it necessary to reduce the size of the cross-pin unit accordingly, which results in the necessity of reducing the torque. By staggering the upper and lower cross-pin units in this way, however, it is made possible to reduce the roll diameter D only, while securing required maximum torque, so that it becomes easy to secure the required pressing amount.

When the value of D/P is equal to or less than 0.55, the cross-pin units 33 and 43 may interfere with the protruding portions 6 a and 8 a of the shafts of the upper leveling rolls 6 and the lower leveling rolls 8. For this reason, the value of D/P is preferably greater than 0.55 and more preferably greater than 0.6. When the relation, D/P<0/9, is satisfied, the effect of increasing the pressing amount is achieved. In view of achieving the effect more reliably, the value of D/P is preferably less than 0.8 and more preferably less than 0.7.

Next, results of experiments will be described, in which leveling or flattening of steel sheet material was performed when the roll diameter of the leveling rolls was 360 mm (D/P=0.923), which is within the conventional range, and when the roll diameter of the leveling rolls was 260 mm (D/P=0.667), under the conditions where the maximum yield stress was 1400 MPa, the corresponding maximum sheet-material thickness was 26 mm, and the roll pitch of the leveling rolls was correspondingly set at 390 mm. Note that the torque was the same in both cases. FIG. 8 shows a diagram, in which the abscissa indicates sheet-material thickness and the ordinate indicates yield stress, showing a region, in which flattening can be performed when the plastification ratio is 70% (0.7). As shown in this figure, it can be found that, when the value of D/P is reduced by reducing the roll diameter to 260 mm, the region, in which flattening can be performed, extends to the direction of thin thickness and high yield stress as compared to the case where the roll diameter is 360 mm. This is because the maximum pressing amount is 50 mm when the roll diameter is 360 mm, whereas the maximum pressing amount increases to 80 mm when the roll diameter is 260 mm. It has been found that, since such a large pressing amount is achieved, it becomes possible to perform leveling or flattening of sheet material that is thinner and greater in yield stress.

As described above, when the value of D/P is reduced below 0.9, it is made possible to give a high degree of bending to the sheet material by increasing the pressing amount and it is made easy to perform leveling or flattening of sheet material that is thin and high in yield stress. However, components, such as an upper frame and a lower frame, are in some cases deflected (lateral deflection) in a lateral direction (the lateral direction means those of the frame, etc.: Since these lateral directions are parallel with the lateral direction of the sheet material and therefore, these directions have the same meaning). In such a case, the pressing amount varies in the lateral direction because of the lateral deflection. In this embodiment, in order to eliminate the influence of such lateral deflection, the deflection amounts of the upper and lower frames 2 and 3 are determined based on the detected values from the deflection-detecting sensors 21 and/or 22, and the required tightening amounts of the hydraulic crowning cylinders 12 that are required to compensate for the deflection amounts are calculated to perform crowning correction of the upper leveling rolls 6 based on the required tightening amounts. In this way, it is made possible to reduce variations in the penetration amounts in the lateral direction of the sheet material S to be flattened and it is therefore possible to perform flattening with a higher degree of flatness.

Based on the information on compressive deformation of the pressing cylinders 4 a and 4 b, the hydraulic crowning cylinders 12, the upper roll frame 5, the upper backup rolls 7, the upper leveling rolls 6, the lower leveling rolls 8, the lower backup rolls 9, and the lower roll frame 10 that is obtained through the load cells (or hydraulic pressure converters) 23 installed between the housing 1 and the pressing cylinders 4 a and 4 b, the required tightening amounts of the hydraulic crowning cylinders 12 that are required to compensate for the compressive deformation may be calculated in addition to the required tightening amounts of the hydraulic crowning cylinders 12 that are required to compensate for the amounts of lateral deflection of the upper frame 2 and the lower frame 3. The crowning correction of the upper leveling rolls 6 may then be performed based on the total value obtained by summing both the required tightening amounts. In this way, it is made possible to further reduce variations in the penetration amounts in the width direction of the sheet material S to be flattened and it is therefore possible to perform flattening with a further higher degree of flatness.

The official gazettes of Japanese Patent No. 3443036 and Japanese Patent No. 3726146 describe such crowning correction in detail and the descriptions of these official gazettes shall be incorporated into this specification.

Next, correction control for catching will be described.

As described above, the pressing amount (penetration amount) for the pressing cylinders 4 a and 4 b that is required to level (flatten) the sheet material S is set in the control unit 60 and the flattening of the sheet material S is performed according to the specified pressing amount (penetration amount). When the specified pressing amount (penetration amount) set for the entrance-side pressing cylinders (pressing cylinders 4 a when the transfer direction of the sheet material S is the direction A) exceeds catch limit pressing amount that is a limit value, at or under which the sheet material is caught, a failure in catching the sheet material S between the upper leveling rolls 6 and the lower leveling rolls 8, that is, a catch failure occurs. Especially when the diameter of leveling rolls is reduced as in the case of the present embodiment as compared to conventional cases to increase the pressing amount, a catch failure occurs more easily.

In such a case, therefore, the occurrence of a catch failure is prevented by performing the correction control for catching based on the catch correction table in FIG. 7. Note that specific numerals are in actuality entered in the catch correction table in FIG. 7.

Specifically, the pressing-and-catching controller 66 of the control unit 60 compares the specified pressing amount δe1 of the entrance-side pressing cylinders set according to conditions, such as sheet-material thickness, and the catch limit pressing amount δL corresponding to the range of the sheet-material thickness of the sheet material S in the catch correction table in FIG. 7 with each other before the sheet material S is caught between the upper leveling rolls 6 and the lower leveling rolls 8 of the leveling roll unit 20. When the specified pressing amount δe1 exceeds the catch limit pressing amount δL, catch correction mode is entered.

Specifically, as shown in FIG. 9, when the specified pressing amount δe1 exceeds the catch limit pressing amount δL, the actual pressing amount of the entrance-side pressing cylinders at the time of catching the sheet material S is changed from the specified pressing amount δe1 and limited to the catch limit pressing amount δL. Such limitation of the pressing amount is continued until the sheet material S is caught and the leading edge of the sheet material S reaches a distance of Lb, set in the correction table in FIG. 7, from the peak of the reference leveling roll (the leveling roll #1 in FIG. 9). As shown in FIG. 10, after the sheet material S is caught and the leading edge of the sheet material S reaches a distance of Lb from the entrance-side reference leveling roll, the pressing amount (penetration amount) of the entrance-side pressing cylinders is set to the specified pressing amount δe1 at the pressing correction speed IV entered in the catch correction table. Note that in FIGS. 9 and 10, the reference leveling roll closest to the entrance side is numbered #1, and the remaining rolls are numbered #2 to #9 in order from left to right.

In general, at the time of catching the sheet material S, the sheet material S is caught between the upper and lower leveling rolls when the pressing amount is equal to the catch limit pressing amount δL, which is almost proportional to the thickness of the sheet material S. Once the sheet material S is caught by a certain length, no catch failure occurs even when the pressing amount is increased above the catch limit pressing amount δL. For this reason, when the catch limit pressing amount δL is entered in the catch correction table and the above certain length is entered as the catch correction control distance Lb for each sheet-material thickness of the sheet material S, it is made possible to swiftly perform setup of the leveling rolls to the specified pressing amount δe1 to flatten the sheet material S while reliably preventing the catch failure. As a result, it is made possible to keep high the yield of the sheet material S after flattening.

The pressing correction speed IV is the speed of change from the catch limit pressing amount to the specified pressing amount δe1. Since an appropriate value of the pressing correction speed IV depending on the thickness of the sheet material S exists, it is possible to perform setup of the leveling rolls to the specified pressing amount δe1 at an optimum speed by entering the press correction speed IV in the correction table in advance.

When the diameter of the leveling rolls is set small to increase the pressing amount as in this embodiment, it becomes very difficult to catch the sheet material S between the upper and lower leveling rolls. However, by performing the correction control for catching as described above, it is made possible to relatively easily catch the sheet material S between the upper and lower leveling rolls even in this case. For this reason, the correction control for catching is effective especially when the pressing amount is large as in this embodiment.

When such correction control for catching is performed, light pressing corresponding to the catch limit pressing amount δL is performed first, and then the operation is shifted to strong pressing corresponding to the specified pressing amount δe1. As such, when the specified pressing amount δe1 is large as in this embodiment, it is feared that the uniformity of roll gaps in the width direction of the leveling rolls because of the lateral deflection etc. of the upper frame 2 and the lower frame 3 is reduced. However, as described above, by performing the crowning correction using the deflection-detecting sensors 21 and 22 and the hydraulic crowning cylinders 12, it is made possible to keep favorable uniformity of roll gaps in the width direction and it is also made possible to reliably perform the correction control for catching even when the specified pressing amount δe1 is large.

The present invention is not limited to the above embodiment and various modifications can be made. For example, while a case where the form of the sheet material is flattened by pressing (pushing downward) the upper leveling rolls toward the pass line with the use of the pressing cylinders has been described in the above description of the embodiment, the form of the sheet material may be flattened by pressing (pushing upward) the lower leveling rolls toward the pass line with the use of pressing cylinders. Those obtained by omitting part of the components of the above embodiment without departing from the scope of the present invention also fall within the scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1; housing     -   2; upper frame (working frame)     -   3; lower frame     -   4 a, 4 b; pressing cylinder (pushing cylinder)     -   5; upper roll frame     -   6; upper leveling roll     -   6 a, 8 a; protruding portion of shaft     -   7; upper backup roll     -   8; lower leveling roll     -   9; lower backup roll     -   10; lower roll frame     -   12; hydraulic crowning cylinder     -   15; driving mechanism     -   21, 22; deflection-detecting sensor     -   30; upper leveling roll-driving section     -   31, 41; universal spindle     -   32, 42; driving motor     -   33, 34, 43, 44; cross-pin unit     -   35, 45; intermediate shaft     -   60; control unit     -   64; crowning controller     -   66; pressing-and-catching controller     -   100; roller leveler     -   S; sheet material (sheet material to be flattened) 

1. A roller leveler for flattening sheet material by passing the sheet material through a pass line, comprising: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a pushing cylinder configured to press the sheet material via the leveling rolls and provided on each of an entrance side and a discharge side of the leveling roll unit, on which the sheet material enters and is discharged into and from the leveling roll unit, respectively; a plurality of backup rolls that back up the leveling rolls; and a driving mechanism configured to rotate the leveling rolls to pass the sheet material, wherein the plurality of leveling rolls are designed so that a diameter D thereof satisfies a relation, 0.5<D/P<0.9, in relation to a roll pitch P of the leveling rolls that is determined from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material.
 2. The roller leveler according to claim 1, further comprising a control unit that is configured to control an amount of pressing of the sheet material performed by the pushing cylinder so that the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, wherein the control unit has a catch correction table, in which a catch limit pressing amount and a catch correction control distance depending on thickness of the sheet material are entered, the catch limit pressing amount being a pressing amount, at or under which the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, the catch correction control distance being an amount of travel of a leading edge of the sheet material, at which the pressing amount should be brought to the catch limit pressing amount, and the control unit is configured so that when a specified pressing amount, required to flatten the sheet material, of the pushing cylinder on the entrance side is greater than the catch limit pressing amount, the control unit performs control based on the catch correction table so that the pressing amount of the pushing cylinder on the entrance side is limited to the catch limit pressing amount until the leading edge of the sheet material reaches the catch correction control distance and, when the leading edge of the sheet material reaches the catch correction control distance, the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount.
 3. The roller leveler according to claim 2, wherein pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance, is entered in the catch correction table, and wherein the control unit controls the pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is changed from the catch limit pressing amount to the specified pressing amount, based on the catch correction table.
 4. A roller leveler for flattening sheet material by passing the sheet material through a pass line, comprising: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a plurality of backup rolls that back up the plurality of leveling rolls from upper and lower sides; a pair of roll frames that support the leveling rolls and the backup rolls from upper and lower sides; a pair of frames that support the pair of roll frames from upper and lower sides; a pushing cylinder provided on each of an entrance side and a discharge side, at which the sheet material enters and is discharged into and from the leveling roll unit, respectively, and configured to push a working frame, which is one of the pair of frames, toward the pass line so as to press the sheet material between the leveling rolls via a corresponding one of the pair of roll frames; a driving mechanism configured to rotate the leveling rolls; a plurality of hydraulic crowning cylinders installed so as to be lined up in a width direction perpendicular to a direction, in which the sheet material is passed, between the working frame and the corresponding one of the pair of roll frames; and a control unit that controls flattening of the sheet material, wherein the plurality of leveling rolls are designed so that a diameter D thereof satisfies a relation, 0.5<D/P<0.9, in relation to a roll pitch P of the leveling rolls that is determined from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material, and the control unit is configured to perform control so that the sheet material is passed between the leveling rolls via the driving mechanism while controlling an amount of pressing performed by the pushing cylinders, and is also configured to perform tightening control, in which amounts of lateral deflection of the pair of frames in the width direction are determined, a required amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the amounts of lateral deflection is calculated, and tightening of each of the hydraulic crowning cylinders is controlled based on the required amount of tightening.
 5. The roller leveler according to claim 4, wherein, based on information on compressive deformation of the pushing cylinders, the hydraulic crowning cylinders, the pair of roll frames, the backup rolls, and the leveling rolls, the control unit calculates a required amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the compressive deformation and performs the tightening control of each of the hydraulic crowning cylinders based on a total value obtained by summing both this required amount of tightening and the required amount of tightening that is required to compensate for the amounts of lateral deflection of the pair of frames.
 6. The roller leveler according to claim 4, wherein the control unit has a catch correction table, in which a catch limit pressing amount and a catch correction control distance depending on thickness of the sheet material are entered, the catch limit pressing amount being a pressing amount, at or under which the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, the catch correction control distance being an amount of travel of a leading edge of the sheet material, at which the pressing amount should be brought to the catch limit pressing amount, and the control unit is configured so that when a specified pressing amount, required to flatten the sheet material, of the pushing cylinder on the entrance side is greater than the catch limit pressing amount, the control unit performs control based on the catch correction table so that the pressing amount of the pushing cylinder on the entrance side is limited to the catch limit pressing amount until the leading edge of the sheet material reaches the catch correction control distance and, when the leading edge of the sheet material reaches the catch correction control distance, the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount.
 7. The roller leveler according to claim 6, wherein pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance, is entered in the catch correction table, and wherein the control unit controls the pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is changed from the catch limit pressing amount to the specified pressing amount, based on the catch correction table.
 8. The roller leveler according to claim 1, wherein the diameter D and the pitch P satisfy a relation, 0.55<D/P<0.8.
 9. The roller leveler according to claim 1, wherein the driving mechanism includes: an upper leveling roll-driving section that has upper leveling roll-driving motors for driving the upper leveling rolls and upper leveling roll power-transmitting part for transmitting power of the upper leveling roll-driving motors to the upper leveling rolls; and a lower leveling roll-driving section that has lower leveling roll-driving motors for driving the lower leveling rolls and lower leveling roll power-transmitting part for transmitting power of the lower leveling roll-driving motors to the lower leveling rolls, wherein the upper leveling roll power-transmitting part and the lower leveling roll power-transmitting part are disposed so as not to interfere with each other.
 10. The roller leveler according to claim 9, wherein the upper leveling roll power-transmitting part is a universal spindle that includes: a first upper cross-pin unit connected to the upper leveling roll-driving motor side; a second upper cross-pin unit connected to a protruding portion of a shaft of each of the upper leveling rolls; and an intermediate shaft connecting the first and second upper cross-pin units, wherein the lower leveling roll power-transmitting part is a universal spindle that includes: a first lower cross-pin unit connected to the lower leveling roll-driving motor side; a second lower cross-pin unit connected to a protruding portion of a shaft of each of the lower leveling rolls; and an intermediate shaft connecting the first and second lower cross-pin units, and wherein a length of the protruding portion of the shaft of each of the upper leveling rolls and a length of the protruding portion of the shaft of each of the lower leveling rolls differ from each other so that the second upper cross-pin unit and the second lower cross-pin unit do not interfere with each other.
 11. (canceled)
 12. A sheet-material flattening method of flattening sheet material via a roller leveler for flattening the sheet material by passing the sheet material through a pass line, wherein the roller leveler includes: a leveling roll unit that has a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the sheet material while flattening the sheet material interposed therebetween; a plurality of backup rolls that back up the plurality of leveling rolls from upper and lower sides; a pair of roll frames that support the leveling rolls and the backup rolls from upper and lower sides; a pair of frames that support the pair of roll frames from upper and lower sides; a pushing cylinder provided on each of an entrance side and a discharge side, at which the sheet material enters and is discharged into and from the leveling roll unit, respectively, and configured to push a working frame, which is one of the pair of frames, toward the pass line so as to press the sheet material between the leveling rolls via a corresponding one of the pair of roll frames; a driving mechanism configured to rotate the leveling rolls; and a plurality of hydraulic crowning cylinders installed so as to be lined up in a width direction perpendicular to a direction, in which the sheet material is passed, between the working frame and the corresponding one of the pair of roll frames, the method comprising: determining a roll pitch P of the plurality of leveling rolls from a maximum requirement yield stress and a maximum requirement sheet-material thickness of the sheet material to be flattened; setting a value of diameter D of the plurality of leveling rolls so as to satisfy a relation, 0.5<D/P<0.9; determining amounts of lateral deflection of the pair of frames in the width direction; calculating an amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the amounts of lateral deflection; and controlling tightening of each of the hydraulic crowning cylinders based on the required amount of tightening.
 13. The sheet-material flattening method according to claim 12, further comprising: based on information on compressive deformation of the pushing cylinders, the hydraulic crowning cylinders, the pair of roll frames, the backup rolls, and the leveling rolls, calculating a required amount of tightening of each of the hydraulic crowning cylinders that is required to compensate for the compressive deformation; and controlling tightening of each of the hydraulic crowning cylinders based on a total value obtained by summing both this required amount of tightening and the required amount of tightening that is required to compensate for the amounts of lateral deflection of the pair of frames.
 14. The sheet-material flattening method according to claim 12, wherein, based on a catch correction table, in which a catch limit pressing amount and a catch correction control distance depending on thickness of the sheet material are entered, the catch limit pressing amount being a pressing amount, at or under which the sheet material is caught between the upper and lower leveling rolls of the leveling roll unit, the catch correction control distance being an amount of travel of a leading edge of the sheet material, at which the pressing amount should be brought to the catch limit pressing amount, the following are further performed: limiting the pressing amount of the pushing cylinder on the entrance side to the catch limit pressing amount until the leading edge of the sheet material reaches the catch correction control distance when a specified pressing amount, required to flatten the sheet material, of the pushing cylinder on the entrance side is greater than the catch limit pressing amount; and bringing the pressing amount of the pushing cylinder on the entrance side to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance.
 15. The sheet-material flattening method according to claim 14, further comprising: entering into the catch correction table pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is brought to the specified pressing amount when the leading edge of the sheet material reaches the catch correction control distance; and controlling the pressing speed, at which the pressing amount of the pushing cylinder on the entrance side is changed from the catch limit pressing amount to the specified pressing amount, based on the catch correction table.
 16. The sheet-material flattening method according to claim 12, wherein the diameter D and the pitch P satisfy the relation, 0.55<D/P<0.8. 